Re: Plot failure: "Visible pixel grid has a scan line longer than previous scan lines"

[Ethan A M. <me...@uw...>]

On Monday, 29 June 2020 19:51:04 PDT Dima Kogan wrote:
> Alright, I debugged this (rr was invaluable), and I know mostly what's
> going on. The flow is roughly this:
> 
> 1. The data is read here:
> 
>    https://sourceforge.net/p/gnuplot/gnuplot-main/ci/branch-5-4-stable/tree/src/plot3d.c#l1037
> 
>    At the end of the first line, x is 3999.0000000000005, which is just outside the
>    xrange [0:3999]. This isn't unexpected due to the "using" expression

But the x coordinates should come out identically the same in the "good" and "bad"
cases, right?  So how does this explain a different between them?

	Ethan

> 
> 2. Later we evaluate the x axis for that point (first row, last col):
> 
>    https://sourceforge.net/p/gnuplot/gnuplot-main/ci/branch-5-4-stable/tree/src/axis.c#l2782
> 
>    3999.0000000000005>3999, so we set this to OUTRANGE
> 
>    In a perfect world we should be looking at the "with image" pixel
>    edges instead of just the center; like we do in step 5 below.
> 
> 3. Later we evaluate the z axis for that same point, but this is already
>    OUTRANGE, so we don't bother to use that point to set axis->min or
>    axis->max
> 
> 4. As a result the view_port_z[] range we set later is narrower than it
>    should be:
> 
>    https://sourceforge.net/p/gnuplot/gnuplot-main/ci/branch-5-4-stable/tree/src/graphics.c#l4822
> 
> 5. And then, further on in in that function, that corner pixel is deemed
>    invisible. So the first row then has only 15 pixels, but the next row
>    has all 16, so we complain
> 
> The logic in step 5 (what we do for !visible pixels) looks suspicious,
> but I want to say the fundamental problem is that step 2 and step 5 have
> different logic for inrange/outrange. The top-right corner of the
> failing plot is OUT in step 2, but IN in step 5.
> 
> Any obvious fixes?
> 
> Thanks
> 
> 
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-- 
Ethan A Merritt
Biomolecular Structure Center,  K-428 Health Sciences Bldg
MS 357742,   University of Washington, Seattle 98195-7742